Reverse flotation is a common process applied in the art separating the gangue from the valuable minerals via the froth. Particularly silicate-containing ores like iron ore, calcium carbonate, phosphates and feldspar are concentrated by this process by enriching and removing the silicate impurities, i.e. quartz, mica and feldspar but also muscovite and biotite, in the flotate.
Iron ore commonly contains silicates which have a negative impact on the quality of the iron produced thereof and complicate the production process of high quality steels. Therefore oxidic iron ores, i.e. magnetite, haematite, martite, limonite and goethite, are concentrated by reverse silicate flotation by using alkylether amines and alkylether diamines as typical collectors for silicate minerals.
Fatty amines, alkylether amines, alkylether diamines and quaternary ammonium compounds are known as collectors for silicate containing minerals and are commercialized e.g. under the trade name Flotigam®.
Reverse iron ore flotation is described in U.S. Pat. Nos. 3,363,758, 4,168,227, 4,422,928 and 4,319,987, in which the use of alkyletheramines, alkyletherdiamines, primary amines and mixtures thereof is disclosed. Due to their poor water solubility the application of partially neutralized ammonium acetates is also disclosed.
CA-1 100 239 discloses the use of alkylether monoamines or diamines in combination with an emulsifying agent in a froth flotation process.
U.S. Pat. No. 5,540,337 discloses a process of separating at least one mineral, e.g. silica, from an aqueous medium, which may contain iron ore, by froth flotation using cationic alkyloxyalkaneamine collectors free of acrylonitrile.
U.S. Pat. Nos. 4,732,667 and 4,830,739 disclose a process and composition for the beneficiation of iron minerals from iron ores containing silicate and phosphate minerals, comprising as collector a combination of a primary amine and a nitrogen compound containing an anionic group selected from methylene carboxylic acid, ethylene phosphoric acid and methylene phosphonic acid.
The use of anionic surfactants as co-collectors is also disclosed in U.S. Pat. No. 5,540,336 and EP-A-0 609 257 in combination with at least one alkylether amine or one alkylether diamine. The selective removal of phosphorous impurities without any negative impact on the cationic flotation of the silicate is disclosed.
U.S. Pat. No. 6,076,682 describes a froth flotation process of silica from iron ore by using a collecting agent which contains a combination of an alkylether monoamine with alkylether diamine.
WO-A-00/62937 describes the use of quaternary ammonium compounds in a froth flotation process of silicate from iron ore.
The removal of silicate containing impurities from calcite using methyl-bis(2-hydroxypropyl)-cocosammonium methyl sulfate as flotation reagent is described in U.S. Pat. No. 4,995,965.
U.S. Pat. No. 5,261,539 suggests the application of alkoxylated alkylguanidines and alkoxylated amines in the reverse flotation of calcite.
U.S. Pat. No. 5,720,873 discloses the combination of quaternary ammonium salts with an alkylene oxide adduct of fatty amines for cleaning calcium carbonate ore from silicates. A significant improvement is disclosed in respect of the separation of acid insoluble matter.
The aim of the present invention is to develop a more selective and efficient froth flotation process for the beneficiation and ore concentration of silicate containing minerals and ores. The present invention relates in particular to the reverse flotation process of iron ore and calcite, which results in a high recovery of the valuable mineral as well as in low silica content, but also to the direct flotation of quartz and other silicates.
It has surprisingly been found that the selectivity and efficiency of the froth flotation process can be significantly improved by using a finely dispersed collector agent characterized by a specific droplet size distribution in the nanometer scale.
The state of the art is silent on the preferred droplet size of collectors used during the process of flotation. The flotation process is based on interactions between interfaces of solid, liquid and gas phases. Therefore the size of micelles formed by the collector has a determining significance for the efficiency and selectivity of the concentration during flotation process. Droplet size analysis of ether monoamines and diamines has shown that these standard collectors, which regularly applied in partially neutralized form, are forming micelles in water with an average droplet larger than 30 μm, mostly larger than 250 μm. The simple combination of those ether amines with an emulsifiying agent as disclosed by CA-1 100 239 yield unstable, quickly coalesced emulsions whose droplet size can not by determined (see Table 2).
Alkylether monoamines and diamines can be finely dispersed in conjunction with nonionic, anionic or cationic surfactants by using a mechanical high-pressure-homogenizer of the Gaullin type at pressures up to 1500 bar to give stable emulsions showing a droplet size in the range of 1 nm to 20 μm. To achieve the very small droplet size required herein, the emulsion of the collector has to be passed at least one time through the high-pressure homogenizer. If necessary, the passing through the high pressure homogenizer has to be repeated until such particle size is reached. Surprisingly it was found that these collector emulsions of nanometer scale exhibit advantageous properties regarding selectivity and iron recovery in the reverse iron ore flotation which distinguishes them from conventional products. Thus, we have observed that the general metallurgical performance of a collector, i.e. selectivity and recovery, relates directly to its size of micelle in the emulsion.
This invention therefore relates to a nanoemulsion, comprising at least one collector for the flotation of silicate minerals from other minerals, at least one emulsifier, and water, wherein water forms the continuous phase and the average particle size of the collector which forms the discontinuous phase is from 1 nm to 20 μm.
The invention further relates to a process for the production of a nanoemulsion, comprising at least one collector for the flotation of silicate minerals from other minerals, at least one emulsifier, and water, wherein water forms the continuous phase and the average particle size of the collector which forms the discontinuous phase is from 1 nm to 20 μm, the process comprising the step of passing a mixture of the collector, the emulsifier and water through a mechanical high pressure homogenizer at a pressure from 100 to 1500 bar.
The invention further relates to a process for beneficiation of ores from silicate gangue, the process comprising the steps of bringing the ore into contact with the above-described nanoemulsion and frothing of the so obtained composition.
The nanoemulsion of the invention comprises at least one collector, preferably in the amount of 20 to 60 wt.-%, in particular in the amount of 25 to 50 wt.-%, particularly preferred in the amount of 30 to 40 wt.-%.
The amount of emulsifier in the nanoemulsion is preferably at most 20 wt.-%, particularly at most 10 wt.-%, more preferably at most 5 wt.-%. A preferred lower limit for the amount of emulsifier is 0.1 wt.-%, more preferably 1 wt.-%.
The nanoemulsion preferably contains up to 79.9 wt.-% water, more preferably 20 to 79 wt.-% water, most preferably 30 to 60 wt.-% water.